ARCHIVED REPORTS_FOURTH QUARTER AND ANNUAL 2010 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT

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Stantec L & M OPERABLE UNIT- FOURTH QUARTER AND ANNUAL 2010 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Summary of 2010 Annual Monitoring and Sampling January 31, 2011 5.10 2010 ARSENIC TRENDS In accordance with the MRP for the Site, groundwater sampling for the presence of arsenic was not required during the 2Q10 and 4Q10. Arsenic concentrations in selected shallow and deep zone wells within the hydrocarbon plume and within perimeter wells were evaluated for historical trends on a semi-annual basis during the 1Q10 and 3Q10. During 2010, arsenic detectable concentrations ranged from 0.0078 (MW-23; 1Q10) to 0.34 mg/L (MW-19; 1Q10) in the shallow zone wells, from 0.0080 mg/L (MW-35; 1Q10) to 0.086 mg/L (MW-59; 3Q10) in the B-Zone wells, from 0.0070 mg/L (MW-61; 3Q10) to 0.031 mg/L (MW-54; 3Q10) in the C-Zone wells, and from 0.011 mg/L (MW-70; 1010) to 0.040 mg/L (MW-55; 3Q10) in the D-Zone wells. Arsenic concentrations over the past three years appear to be relatively stable. Graphs depicting arsenic trends in selected shallow and deep zone wells within the petroleum hydrocarbon plume (shallow wells MW-9, MW-32, 2AMW-13, DPE-9, and deep zone well MW-17) and shallow and deep well pairs along the perimeter of the dissolved plume (MW-34/MW-35, MW-25/MW-26, and MW-27/MW-28) are included in Appendix F. Arsenic trends will continue to be evaluated during the 1 Q1 1 and 3Q11. 5.11 2010 ANNUAL SITE SUMMARY Groundwater elevations, groundwater gradient, and chemical concentrations throughout 2010 were generally consistent with historical data. The area of greatest impact to groundwater by petroleum hydrocarbons, in the shallow zone wells, is centered in the vicinity of well 2AMW-14 and the DPE wells, which have consistently reported the presence of SPH. Petroleum hydrocarbon impacts and SPH in this area are currently addressed with the operation of the DPE/ASVE/SVE system. The area of greatest petroleum hydrocarbon impact within the deep zone wells is found off Site in the southern section of the Water Front Towers' parking lot, in wells MW-43, MW-47, MW-48, MW-49 and MW-50, and in the northern section of the L&M OU site, in wells MW-17 and MW-52, which have contained measurable SPH or sheen since their installation. SPH in this area is currently addressed with quarterly (at a minimum) extraction events. The shallow impacted groundwater plumes are generally delineated to the south, west, and north by the current well network and the Deep Water Channel. The deeper impacted groundwater plumes are generally delineated to the south and west. Additional assessment is needed to define the plumes originating east of the Site at the UOU and MOU. All accessible petroleum hydrocarbon-impacted soil has been removed from the L&M OU and off-site to the north in the Water Front Towers' parking lot as a result of pipeline removal and soil over-excavation activities conducted on behalf of the L&M OU Group, except for a small portion of impacted soil that remains beneath the on Site remediation compound which existed prior to excavation activities. Additional assessment and remedial activities have also been performed by the SRDA to address contaminated soil and remaining pipelines east of the site at the UOU and MOU, and north of the site to the west and north of the Waterfront Towers parking lot. The results of the UOU and MOU excavations are included in Treadwell and Rollo's Removal Action Completion Report Unocal Operable Unit on Area 2A dated August 5, 2009 and the results of the excavation north of the site and to the west and north of the Waterfront Towers parking facility are in Wallace Kuhl's Underground Storage Tank Removal Report Former North Edison Street dated June 8, 2009. I:\Tidewater\TW Stockton(Parcel 2A-0415)\Reports\QMR\2010\4010-Annual\4Q10 and Annual OSSRQRSRQMR Stockton_FINAL.doc 5.8